For a digital video distribution system, the video is encoded and decoded using a series of video frames. Furthermore, in a digital video receiver device, such as an LCD TV, a series of video frames is decoded from the compressed video stream and further processed before final rendering on the display. Frame rate conversion (FRC) is a video processing method to convert the frame rate of a video stream, for example from 24 frames per second to 60 frames per second (fps), or from 60 fps to 120 fps. In frame rate conversion, new video frames are generated in addition to or in place of the input video frames, where the new frames may be rendered at time instances different from the time instances that the input frames are rendered. Frame rate conversion techniques may generate new video frames by combining adjacent video frames, for example by frame repetition or frame averaging. Higher video quality can be achieved by utilizing motion estimation and motion compensation techniques for frame rate conversion. This method is also known as motion-compensated frame interpolation. Motion estimation and motion compensation for frame rate conversion is conventionally carried out on a block by block basis.
Digital video content often contains textual and graphical elements that are overlaid onto or blended into the underlying camera-captured natural video frames. Digital video content, such as that available from over-the-air broadcast television, cable television, Internet based videos, etc., often presents a logo. For example, a television broadcast may include the broadcasting network and the broadcasting station logo in a lower right hand corner of the broadcast to indicate its source. In some situations, the broadcast has the logo image completely overlaying the underlying broadcast video content. In other situations, the broadcast logo image may be semi-transparent overlaying the underlying video content. The logo often remains in the video frames being displayed during all or a substantial portion of the program. In some cases, the logos include advertising content for the program. In addition, digital video content often contains text that is either static or moving with constant speed, such as movie credits, sliding or scrolling news updates, and other informational text and graphics. Broadcast channel logos, moving text, and similar graphical video elements represent a challenge for video frame rate conversion methods utilizing conventional motion estimation and motion compensation methods. Often, estimated motion vectors near the channel logo or moving text are not accurate. Hence, regions containing or near graphical and textual overlays in the motion compensated frames are likely to contain artifacts, may have temporal jitter and may appear temporally unstable.
The textual and graphical regions of the frames tend to be visually important to the viewing experience. The nature of the textual and graphical regions are typically included with an overlay on the underlying background video in a manner such that the textual and graphical regions have sharper edges than the background content. With the sharper edges and the visual importance of the textual and graphical regions any artifacts as a result of motion estimation and motion compensation of such regions tend to be readily noticeable by the viewer. Unfortunately, the traditional motion estimation and motion compensation techniques tend to result in inferior results.
The foregoing and other objectives, features, and advantages of the invention may be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.